Research

Understanding how global climate change impacts ecosystem structure and function is one of the greatest scientific challenges of our time. Examining how trees and forests respond to environmental change is of particular importance due to their critical role in supporting biodiversity, regulating global carbon, water, and nutrient cycles, and providing a multitude of ecosystem and social services.

Climate-related impacts have already been observed in diverse forests around the world, and are expected to become more widespread and intense in the coming decades. Projected future climate changes, including higher temperatures and atmospheric carbon dioxide, altered precipitation patterns, greater frequency of extreme events such as heat waves and drought, and shifts in growing seasons, will have profound physical and biological effects on trees and associated forest ecosystems globally.

The overarching goal of my research is to advance our knowledge of the physiological mechanisms controlling tree performance and forest ecosystem responses to climate change. I study how uptake, transport and usage of water and carbon by trees are coordinated, and how they are affected by tree structural properties and by variability in soil and atmospheric conditions. Some questions I seek to help answer include:

How does physiological performance vary within and among trees of different size and age?

What functional traits determine the sensitivity of different tree species to climate changes and how do these traits influence tree distributions?

How do tree physiological processes scale from leaf to landscape scales?

What are the ecosystem consequences of climate impacts and how can management actions mitigate these impacts and improve tree and forest health?

My research in collaboration with other scientists combines diverse methods and tools from the fields of plant physiology, forest ecosystem ecology, stable isotope biogeochemistry, dendrochronology, remote sensing, and micrometeorology. I also utilize advanced rope-based climbing techniques in order to directly study tree and forest canopy structure, function, and biological diversity.

Giant sequoia (Sequoiadendron giganteum) is one of the most iconic species on Earth. However, the sequoias' continued health may be threatened by climate change, particularly severe drought. Since 2015 I have been working with an interdisciplinary team from UC Berkeley, National Park Service, US Geological Survey, and Carnegie Airborne Observatory to understand the physiological mechanisms and spatial patterns of giant sequoia tree and forest drought response from leaf to landscape scales.

All plants need an adequate supply of water to sustain their metabolism, growth and survival, and plant water and carbon relations are fundamentally linked. I have been involved in several projects examining tree water and carbon relations to gain a better understanding of these linkages, and am currently working with researchers from UC and Northern Arizona University to quantify environmental controls on water status and physiology of several conifer and angiosperm trees in California and Arizona.

Increasingly hotter droughts and severe wildfires associated with climate change has led to widespread tree mortality resulting in significant impacts on forest ecosystem biodiversity and function throughout California and western US. I am currently working with an interdisciplinary team from the California Academy of Sciences and the US Forest Service's Pacific Southwest Research Station on a project aimed at improving our ability to increase the resilience of western forests to these impacts using prescribed fire.

The rainforests of southeast Asia are one of the most globally significant biological hotspots, yet are continually threatened by deforestation and developmental pressures and now face new risks from global climate change. In 2016 I joined an international team of researchers and conservationists from the California Academy of Sciences and other institutions to document the biodiversity of an ancient Dipterocarp rainforest on Penang Hill, Malaysia in support of a proposed designation as a UNESCO Biosphere Reserve.

Measuring environmental conditions at relevant spatial and temporal scales is a critical component of research aimed at understanding how the climate is changing and how ecosystems are responding to those changes. I have installed and maintained dozens of climate monitoring systems in forest ecosystems to support my research projects, and am currently working on a state-wide climate and phenology sensor network to support the UC Institute for the Study of Ecological and Evolutionary Climate Impacts.